Hop Compounds: Extraction Techniques, Chemical Analyses, Antioxidative, Antimicrobial, and Anticarcinogenic Effects

Abstract

Hop plants comprise a variety of natural compounds greatly differing in their structure and properties. A wide range of methods have been developed for their isolation and chemical analysis, as well as for determining their antioxidative, antimicrobial, and antigenotoxic potentials. This contribution provides an overview of extraction and fractionation techniques of the most important hop compounds known for their health-promoting features. Although hops remain the principal ingredient for providing the taste, stability, and antimicrobial protection of beer, they have found applications in the pharmaceutical and other food industries as well. This review focuses on numerous health-promoting effects of hops raging from antioxidative, sedative, and anti-inflammatory potentials, over anticarcinogenic features to estrogenic activity. Therefore, hops should be exploited for the prevention and even healing of several prevalent diseases like cardiovascular disorders and various cancer types. New ideas for future studies on hops are finally presented: computational investigations of chemical reactivities of hop compounds, nanoencapsulation, and synergistic effects leading to a higher bioavailability of biologically active substances as well as the application of waste hop biomass from breweries for the production of high-added-value products in accordance with the biorefinery concept.

Keywords: anticarcinogenic effects; antimicrobial effects; antioxidative effects; extraction; hops.

Figure 1

(a) Hop plant (Humulus lupulus L.) growing on a trellis. (b) Tissue cultured hop plant (Humulus lupulus L.). Photos were taken by Dr. Zala Kolenc at the premises of Slovenian Institute of Hop Research and Brewing.

Figure 2

Hop cones of the female hop plant (Humulus lupulus L.). The photo was taken by Prof. Dr. Iztok Jože Košir at the premises of Slovenian Institute of Hop Research and Brewing.

Figure 3

The main groups of compounds found in hops, their (skeleton) chemical structures, and some typical representatives. Chemical structures of all typical representatives of soft and hard resins are collected in supplementary material (Figure S1).

Figure 3

The main groups of compounds found in hops, their (skeleton) chemical structures, and some typical representatives. Chemical structures of all typical representatives of soft and hard resins are collected in supplementary material (Figure S1).

Figure 4

Quantum chemical model of (a) the reactant state and (b) the transition state of the reaction between xanthohumol and cyanoethylene oxide acquired according to the Hartree–Fock method and 6-31G(d) basis set [171]. Carbon atoms are depicted in gray, oxygen atoms in red, nitrogen atoms in blue, and hydrogen atoms in white.